1. Field of the Invention
The present invention relates to a plastic optical product and a plastic lens for spectacles that have an optical multilayer film but which are excellent in heat resistance.
2. Description of Related Art
In order to impart anti-reflection properties and the like to plastic lenses, an anti-reflective film including a metal oxide film is formed on a plastic substrate or on a hard coat film of the substrate. Here, the metal oxide film has a smaller coefficient of thermal expansion than those of the plastic substrate and the hard coat film. On this account, when a large amount of heat is applied to a plastic lens, the metal oxide film cannot follow the deformation of the plastic substrate or the hard coat film due to their comparatively large thermal expansion and this may generate cracks on the anti-reflective film.
In order to improve such characteristics against heat and to impart heat resistance, for example, as disclosed in Japanese Laid-open Patent Application, Publication No. 2009-128820 (JP2009-128820A), it is known that a composite layer including at least two metal oxide layers that contain the same metallic element but have different oxygen contents from each other is included in an anti-reflective film.
However, in the invention disclosed in JP2009-128820A, in order to impart heat resistance while maintaining the anti-reflection properties, the composite layer is disposed away from a substrate side (hard coating side) (via a common anti-reflective multilayer film structure). As a result, the common anti-reflective multilayer film structure cannot follow the deformation due to thermal expansion and the heat resistance is not much improved. In addition, especially in the case of lens for spectacles and the like, a round lens is not used as it is and is usually edged to have a certain outer shape such as an ellipsoidal shape, and then the edged lenses are inserted in a frame to be used. However, the lens in JP2009-128820A cannot be considered to have significantly improved heat resistance after inserted in a frame.
Therefore, an object of the present invention is to provide a plastic optical product and a plastic lens for spectacles that have an optical multilayer film but which are excellent in heat resistance.